1. Field of the Invention
The present invention relates to a control system, an electronic apparatus and an image forming apparatus, for managing the magnitude of the total current supplied to external devices connected via a hub in order to control operation at the time of the connection.
2. Description of Related Art
In recent years, some image forming apparatuses, such as copiers, printers and digital combination apparatuses, are equipped with a USB port, and a system that captures image data stored in an external device, such as a USB memory or a digital still camera, and outputs images has been proposed (see, for example, Japanese Patent Application Laid-Open No. 2004-109765).
In this kind of system, the image forming apparatus serves as a host apparatus and controls the external device serving as a device. The maximum current that can be supplied from one USB port provided in the host apparatus is 500 mA. Hence, in the case that a USB hub is connected to the USB port of the host apparatus and that no power is supplied to the USB hub from an AC adaptor or the like, the total current of the operating current of the USB hub and the currents that can be supplied to multiple USB devices connected to the USB hub is 500 mA.
The present USB specifications stipulate that a maximum current of 500 mA can be supplied from each USB port. Hence, in the case that the current consumption of a USB device to be connected is 500 mA or less, the USB device is configured so as to operate when connected. Because the current consumption of a USB device is generally low, multiple USB devices are frequently operated by only the current supplied from the host, and even when a USB hub is used, no power supply is connected to the USB hub.
However, in the case that a USB device having a high current consumption is connected, problems occur. For example, overcurrent protection is activated inside the USB port or the USB hub, and the USB device having the high current consumption cannot be connected electrically; or the operating voltage of the USB hub is lowered, and the operation of the USB hub itself and the operation of the USB device connected to the USB hub become unstable or impossible. In other words, although the maximum current that can be supplied is 500 mA, in the case that a large capacity device is connected, a large current is supplied to the device, and the above-mentioned problems will occur. As a result, there is a fear of adversely affecting the devices having been connected to the same USB hub.